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Alternator/charging

S

swedish-rocket

Member
Joined
Mar 20, 2006
Location
Cincinnati Ohio
I'm trying to fix my charging system. At idle I'll get 13.8 volts once I start turning on my lights, switches, radio etc. it drops voltage. I got it to drop under 11 volts this way. Is there anything I can check?
 
Assuming this is on an older Volvo with the older style alternator with the replaceable brushes. You can check those brushes.

You can and SHOULD also check the wires (especially the ground) as... if you look back through the threads I've started you can find the one where my car lit on fire on it's own in my driveway and damn near took out my whole neighborhood.
 
My alternator wire burned up on a rainy summer day on the way home from work. Some day i will post the pictures of the carnage. It took out the ground and about a foot or so of the wiring harness. All the way to under the crank pulley from the alternator. I replaced the whole run with a 6 gauge wire from starter to alternator.
 
In answer to your post. Yes, it does seem to be loading down the alternator just a bit more than it should. 13.8v is really the minimum you need for the modern batteries. So unloaded the system is at minimum allowable voltage. Maybe a new regulator. as well as brushes? It happens less often but a rectifier diode can fail and that will cause low voltage and low current output with an alternator.
 
swedish-rocket said:
It's a 1990 Volvo 240 with a internal regulator. Wow on your car. Glad no one got hurt. Sorry on your car loss though.
Click to expand...

Oh don't worry. I put it out. Keep a fire extinguisher in your car people! And I'm not talking about one clamped to your A pillar either lol :lol:

dl242gt said:
My alternator wire burned up on a rainy summer day on the way home from work. Some day i will post the pictures of the carnage. It took out the ground and about a foot or so of the wiring harness. All the way to under the crank pulley from the alternator. I replaced the whole run with a 6 gauge wire from starter to alternator.
Click to expand...

Yep same.
 
First off, where are you measuring the voltage. If you are measuring the voltage at the alternator B+ terminal (battery connection) that is the correct place. Any other location and a bad electrical connection could be responsible for the drop in voltage that you are measuring, not the alternator. As you increase the current load the resistance in a bad connection causes a voltage drop proportional to current flow - hence reduced voltage at increased load. Bad electrical connections can cause heat which can cause the problems identified by others.

If you are measuring and seeing the voltage drop right at the alternator terminal, then you have one of the following
- a bad ground on the alternator (same problem as a bad connection) or
- a bad electrical connection within the alternator, perhaps the rectifier assembly
- the voltage regulator is failing to respond to the drop in voltage.

In the case of the regulator, as the load current increases on the alternator the internal impedances within the alternator cause the terminal voltage to drop. The regulator measures the output voltage and attempts to restore the output to the set point by increasing the voltage applied to the field winding which results in increased field current which boosts the alternator output voltage. On an external regulator alternator it is easy to test the operation of the regulator, not so easy on an internal regulator alternator. Failure to respond to the voltage drop could indicate a regulator problem. In a freak set of circumstances where the alternator has enough residual magnetism to generate some voltage at light load, it might also indicate a brush problem. Pulling the regulator / brush holder out to check for damaged brushes is relatively easy.

Go towards the bottom of the following page:

http://www.240turbo.com/AdjustableVoltage.html

Dave Barton provides a lot of useful information on testing your alternator.
 
Thanks guys! I checked it at the battery terminals and cigarette lighter. It will be kind of hard but doable at the terminals. I was hoping for bad ground but maybe there is a issue with the regulator. I'll check these points soon.

Awesome info again! Thanks!
 
swedish-rocket said:
Thanks guys! I checked it at the battery terminals and cigarette lighter. It will be kind of hard but doable at the terminals. I was hoping for bad ground but maybe there is a issue with the regulator. I'll check these points soon.

Awesome info again! Thanks!
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Money well spent.

https://www.amazon.com/AST-Labs-Cur...coding=UTF8&psc=1&refRID=6201G1XDZ8WKWVN433JJ

51shAd0MFEL._AC_UL160_SR160,160_.jpg
 
billkaz said:
Money well spent.

https://www.amazon.com/AST-Labs-Cur...coding=UTF8&psc=1&refRID=6201G1XDZ8WKWVN433JJ

51shAd0MFEL._AC_UL160_SR160,160_.jpg
Click to expand...

I see a new purchase in the near future. I found I had a older bosch alternator in storage. I installed it and the same thing happened. I have 4 gauge wire to the motor from the alternator. I hooked a battery ground to the alternator battery with a 8ga wire. I may run a wire directly from the + power terminal of the battery to alternator to see if that will correct it. I can't seem to get measure the positive wire on the alternator to ground. Maybe I'll try again later.

Btw I brought both alternators to autozone and they both passed the bench test.
 
The alternator tested good? What were the specs? What current draw are the accessory items that you are running? If you have a high power stereo that alone can cause what you are seeing. The alternator can only supply so much current and if your draw is more than it can handle you go below charge voltage for the battery and have low voltage throughout the system.
 
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All it takes is the headlights and the blower motor to drop the voltage down under 12 volts. I have 340LPH pump but it's not affecting it. The stereo is currently one 5" speaker and a CD player.

I believe both are 80 amp alternators.

No specs were given. Autozone is pass fail machine.
 
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Hmm, the machines usually will test voltage at rated current. So if they are good then something on the car isn't. I would check out the basic power wiring layout. Make sure feeds to the fuse box and dash are all good and clean. They come from the power distribution on the inner left fender. that gets power from a smaller red wire from the positive on the battery. Also the grounding path between engine, body, and battery needs to have a good low resistance path.

When you connect the alternator are you connecting the small red wire to D+? there should be a case ground to the bracket on the engine. The big red goes to B+. some alternators have both a D+, and a D- on the back. D+ is the proper connection for the small red wire. Keep at it, sometimes these electrical issues are more than one bad connection or problem.
 
Maybe try doing voltage drop tests of the cables. Look up what a voltage drop test actually entails. I do it all the time for intermittent no cranks on trucks.
 
dl242gt said:
Hmm, the machines usually will test voltage at rated current. So if they are good then something on the car isn't. I would check out the basic power wiring layout. Make sure feeds to the fuse box and dash are all good and clean. They come from the power distribution on the inner left fender. that gets power from a smaller red wire from the positive on the battery. Also the grounding path between engine, body, and battery needs to have a good low resistance path.

When you connect the alternator are you connecting the small red wire to D+? there should be a case ground to the bracket on the engine. The big red goes to B+. some alternators have both a D+, and a D- on the back. D+ is the proper connection for the small red wire. Keep at it, sometimes these electrical issues are more than one bad connection or problem.
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I got the ground going from the alternator to block with 4ga wire. The small red wire is going to D+ 8mm head bolt. The B+ is coming from the starter I believe that then goes to the battery.
 
ZVOLV said:
Maybe try doing voltage drop tests of the cables. Look up what a voltage drop test actually entails. I do it all the time for intermittent no cranks on trucks.
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I'll probably spend sometime figuring how to check components. I think I'm going to have spend a bit of time hunting this issue down. Thanks for all the info guys!
 
142 covered it well..... but I saw no mention of amperage delivery. Alternators are not fixed output devices.... they charge what the system "needs". Right after a start cycle, the amperage will be peak to restore your battery.....

Low 14s is what you should see, as was mentioned. Grounds grounds grounds, will break your heart. Also, never trust a bolted together front clip for the ground path of those lights mounted thereupon.

Last - if your car came factory with 80A capacity, and you've upsized the fuel pump/stereo, why wouldn't you upgrade to 100A charging? Throw one of the Nippon Denso baby alternators on there......
 
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